Wave-guide impedance elements



March 27, 1956 A. G. FOX

WAVE-GUIDE IMPEDANCE ELEMENTS Original Filed July 30, 1942 1 FIG. 6

INVENTOR By A. 6. FOX

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A TTORNEY haired States Patent WAVE-GUmE MEDAN CE ELEMENTS Arthur G.Fox, Eatontown, N. 3., assignor to Bell Telephone Laboratories,Incorporated, New York, N. Y., a corporation of New York Originalapplication July 30, 1942, Serial No. 452,851, now Patent No. 2,432,093,dated December 9, 1947. Divided and this application January 12, 1952,Serial No. 266,179

24 Claims. (Cl. 33373) This invention relates to guided electromagneticwave transmission and more particularly to impedance elements for waveguides. This application is a division of application Serial No.610,956, filed August 17, 1945, now Patent 2,607,850, issued August 19,1952, which, in turn, is a division of application Serial No. 452,851,filed July 30, 1942, now Patent 2,432,093, issued December 9, 1947.

An object of the invention is to provide series-resonant impedancebranches and parallel-resonant impedance branches for use in Waveguides.

Another object of the invention is to provide means for tuning suchresonant impedance branches.

A uniform metallic sheath with or without a dielectric filler will serveas a guide for suitable electromagnetic waves. In cross section thesheath may be circular, rectangular, or of other shape. For allfrequencies above a minimum, known as the cut-off frequency, the guideacts like a transmission line and has a specific propagation constantand characteristic impedance. For any particular frequency there are aninfinite number of cross-sectional sizes and shapes of guide which willhave the same characteristic impedance.

Shunt reactive elements are obtained by placing partial obstructionsacross the wave guide. For dominant transverse electric waves a shuntreactive element may be provided by a transverse metal partition havinga slit therein which extends substantially from one side to the other.If the slit is perpendicular to the direction of polarization of theelectric field the element is primarily capacitive, and if parallel withthe field the element is primarily inductive. v

In accordance with the present invention an aperture in a transversepartition in a wave guide is proportioned to provide both inductive andcapacitive components in the right amounts to resonate at a particularfrequency. Depending upon the shape of the aperture the resonance thusproduced may be either of the parallel type, offering a high shuntimpedance across the guide, or of the series type, offering a low shuntimpedance. For example, a rectangular aperture may be proportioned forparallel resonance or, if made sufficiently narrow, for seriesresonance. The resonance may be sharpened by providing inwardlyextending projections on opposite sides of the opening. A wider openingmay be used if the opposed edges of the aperture are made thicker, or ifthe two halves of the partition are made to overlap. The resonantfrequency may be controlled by adjusting an effective dimension of theaperture or by controlling its eiiective configuration.

The nature of the invention will be more fully understood from thefollowing detailed description and by reference to the accompanyingdrawings, in which like ref erence characters refer to like parts and inwhich:

Figs. 1 and 2 are perspective views of wave guides having thereinpartitions with apertures which provide reactive elements;

Fig. 3 shows a wave-guide termination employing a parallel-resonantelement;

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Fig. 4 shows an impedance element in accordance with the invention thatmay be adjusted for either parallel or series resonance; and

Figs. 5 and 6 show series-resonant elements in accordance with theinvention.

Taking up the figures in more detail, Fig. 1 is a perspective view of asection of a metallic wave guide 1 in the form of a rectangular sheathwhich has, been crosssectioned just ahead of the transverse metallicpartition comprising an upper portion 2 and a lower portion 3 with anaperture 4 therebetween extending from one side of the guide to theother. If the guide 1 is carrying dominant transverse electric waveswith the electric field E polarized in a direction perpendicular to thelength of the aperture 4, as indicated by the arrow, the partition willprovide a shunt capacitive reactance. The magnitude of this reactancedepends upon the width of the aperture 4 in the direction of theelectric field E and decreases as the Width is decreased.

Fig. 2 is similar to Fig. 1 except that the aperture 4 extends from thetop to the bottom of the guide 1 and has its length parallel to thedirection of the electric field E. A partition of this type provides ashunt inductive reactance, the magnitude of which also decreases as thewidth of the aperture 4 decreases. A By properly proportioning theaperture, a partition in a wave guide may be made to provide bothinductive and capacitive components in the right amounts to resonate ata particular frequency. This may be either a parallel resonance or aseries resonance. For example, Fig. 3 shows a parallel-resonant element,that is, one providing a high shunt impedance, in a rectangular waveguide 1. The partition 11 has a symmetrically placed aperture 12 havinga height V in a direction parallel to the. electric field E and a widthW perpendicular thereto. There are an infinite number of differentapertures which will produce parallel resonance but, once either theheight V or the width W has been chosen, the other dimension is therebydetermined. The line 13 gives the locus of the upper right-hand corner14 of all possible rectangular apertures that will provide parallelresonance in the. wave guide 1. Such an element placed in the guide. andfollowed by a solid metallic partition such as 15 placed one-quarter ofa wavelength behind the element 11 will serve as a reflectionlesstermination for the guide 1.

Fig. 4 shows a circular guide 7 having therein an impedance elementwhich may be adjusted for either parallel resonance or series resonance.The partition 16 has a rectangular aperture into which project a pair ofthreaded studs 17 having their axes along a diameter of the guide 7 andparallel to the electric field E. The two internally threaded sleeves18, each with a circular metal plate 19 fastened to one end, may bescrewed onto the studs 17. The separation between the plates 19, andtherefore the resonant frequency of the element, may thus be adjusted asdesired. For series resonance, only a small separation is required. Forparallel resonance the spacing will be greater, and in this case theplates 19 may not be required. An advantage of using an aperture withone or more inwardly extending projections, as shown in Fig. 4,

is that sharper resonances may be obtained.

Fig. 5 shows an element more particularly adapted for series resonance,providing a low shunt impedance. The partition 16 has a symmetricalaperture 20 having its length perpendicular ot the electric field E andits width constricted toward the center by means of the inwardlyextending projections 21 and 22, to which are attached, on oppositesides of the partition 16, two overlapping metal flaps 23 and 24. Theseflaps 23 and 24 may be bent toward or away from each other to adjust thespacing.

therebetween and thereby the resonant frequency of the element.

Fig. 6 shows a modification'of the series-resonant element of Fig. inwhich the flaps 23 and 24 are replaced by two opposing metallic plates25 and 26 which are perpendicular to the partition 16 and attached tothe ends of the projections 21 and 22. 7

Since a metallic obstruction in a wave guide usually produces a point oflowpotential and high current, it is preferable that the partitions besecured to the walls of the guide by soldering, welding, or in someother appropriate manner such that a good electrical contact isobtained. It should also be noted that thinner partitions than thoseshown in the drawings will, under some circumstances, produce moresatisfactory results. The partitions have been shown thicker in thedrawings only in the interest of clarity. In Figs. 3, 4, 5 and 6 aportion of the wave guide has been cut away to show the partitions moreclearly.

It is to be understood that the above-described arrangements areillustrative of the application of the principles of the invention.Numerous other arrangements may be devised by those skilled in the artwithout departing from the spirit and scope of the invention.

What is claimed is:

1. In combination, a conductively sheathed wave guide, means forestablishing electromagnetic waves therein, a transverse partitionwithin said guide, said partition having an aperture which is resonantat the frequency of said waves, two opposite projections and opposedplates at the inner ends thereof which constrict the width of saidaperture and form a comparatively narrow central opening and a wideropening at each end thereof, and means for adjusting the spacing betweensaid plates.

2. The combination in accordance with claim 1 in which said projectionsextend in a direction parallel to the electric field of said waves.

3. The combination in accordance with claim 1 in which said aperture isseries resonant at said frequency.

4. In combination, a hollow-pipe wave guide, a conductive transversepartition therein, said partition containing an aperture which isdimensioned for resonance at a frequency freely transmissible by saidguide, a pair of opposed projections extending from opposite sides ofsaid aperture to form a comparatively narrow central opening and a wideropening at each end thereof, means for increasing the capacitancebetween the inner ends of said projections, and means for adjusting aneffective dimension of said aperture to control the frequency at whichsaid aperture is resonant.

5. The combination in accordance with claim 4 in which said aperture isseries resonant at said frequency.

6. In combination, a conductively sheathed guide for for thetransmission of electromagnetic waves, a partition transversely disposedat a point in said guide, said partition containing an aperturedimensioned to provide at said i point a shunt impedance which isresonant at a frequency transmissible by said guide, a pair of opposedprojections extending from opposite sides of said aperture in adirection parallel to the electric field of said Waves to form acomparatively narrow central opening and a wider opening at each endthereof, means for increasing the capacitance between the inner ends ofsaid projections, and means for adjusting the effective configuration ofsaid aperture to adjust said resonant frequency.

7. The combination in accordance with claim 6 in which said aperture isseries resonant at said frequency.

8. In combination, a conductively sheathed guide for the transmission ofelectromagnetic Waves and a partition transversely disposed in saidguide, said partition having an aperture which is resonant at afrequency transmissible by said guide, and said aperture comprising acomparatively narrow, adjustable central opening and a wider opening ateach end thereof.

9. The combination in accordance with claim 8 in which said aperture isseries resonant at said frequency.

10. In combination, a metallic pipe-shaped wave guide, means forestablishing electromagnetic waves therein, a partition substantiallyperpendicular to the direction of propagation of said waves, saidpartition being provided with an aperture which is resonant at thefrequency of said waves, a pair of opposite projections and opposedplates at the inner ends thereof which constrict the width of saidaperture in a direction parallel to the electric field of said waves andform a comparatively narrow central opening and a wider opening at eachend thereof, and means for adjusting the spacing between said plates.

. 11. The combination in accordance with claim 10 in which said apertureis series resonant at said frequency.

12. In combination, a hollow-pipe wave guide, means for establishingelectromagnetic waves therein, a metallic wall member associated withsaid guide, said member being positioned transversely to the directionof wave I propagation through said guide and having an opening which isresonant at the frequency of said waves, a pair of opposed projectionsextending into said opening from opposite sides thereof in a directionparallel to the electric field of said waves to form a comparativelynarrow central opening and a wider opening at each end thereof,

means at the inner ends of said projections for increasing thecapacitance therebetween, and means for adjusting said capacitance toadjust said resonant frequency.

13. The combination in accordance with claim 12 in which said opening isseries resonant at said frequency.

14. In combination, a pipe-like wave guide, means for establishingelectromagnetic waves therein, a wall member substantially perpendicularto the longitudinal axis of said guide, said member having an aperturedimensioned to be resonant at the frequency of said waves, a pair ofopposed projections extending into said aperture from opposite sidesthereof in a direction parallel to the electric field of said waves toform a comparatively narrow central opening and a wider opening at eachend thereof, a pair of opposed plates connected, respectively, to theinner ends of said projections, and means for controlling an effectivedimension of said aperture to control said resonant frequency.

15. The combination in accordance with claim 14 in which said apertureis series resonant at said frequency.

16. In combination, a wave guide of the hollow-pipe type, exciting meansfor establishing electromagnetic waves therein, a metallic Wallpositioned in said guide, said wall lying in a plane substantiallytransverse to the direction of propagation of said waves and beingprovided with an aperture which is resonant at the frequency of saidexciting means, a pair of opposed projections extending into saidaperture from opposite sides thereof in a direction parallel to theelectric field of said waves to form a comparatively narrow centralopening and a wider opening at each end thereof, means at the inner endsof said projections for increasing the capacitance therebetween, andmeans for adjusting said capacitance to adjust said resonant frequency.

17. The combination in accordance with claim 16 in which said apertureis series resonant at said frequency.

18. In combination, a metallic pipe-shaped wave guide, means forestablishing electromagnetic waves therein, a radiative wallsubstantially perpendicular to the direction of propagation of saidwaves, said wall'being pro: vided with an aperture which is resonant atthe frequency of said waves, a pair of opposed projections extendinginto said aperture from opposite sides thereof in a direction parallelto the electric field of said waves to form a comparatively narrowcentral opening and a wider opening at each end thereof, a pair ofopposed plates connected, respectively, to the inner ends of saidprojections, and means for adjusting the spacing between said plates toadjust said resonant frequency.

19. The combination in accordance with claim 18 in which said apertureis series resonant at said frequency. H

20. In combination, a hollow-pipe wave guide, a transverse partitiontherein, said partition having an aperture, and adjustable means forconstricting the width of said aperture near its center, said meanscomprising a pair of oppositely disposed threaded studs projecting intosaid aperture and a pair of internally threaded sleeves screwed ontosaid studs.

21. In combination, a hollow-pipe wave guide, a transverse partitiontherein, said partition having an aperture, and adjustable means forconstricting the width of said aperture near its center comprising apair of oppositely disposed threaded studs projecting into saidaperture, a pair of internally threaded sleeves screwed onto said studs,and a pair of metal plates fastened to the opposed ends of said sleeves.

22. In combination, a hollow-pipe wave guide, a transverse partitiontherein, said partition having an aperture, and adjustable means forconstricting the width of said aperture near its center, said meanscomprising a pair of overlapping metallic flaps.

23. The combination in accordance with claim 22 in which the spacingbetween said flaps and the area of overlap are selected to make saidaperture series resonant at a frequency freely transmissible by saidguide.

24. In combination, a conductively sheathed wave guide, means forestablishing electromagnetic waves therein, a transverse partitionwithin said guide, said partition having an aperture which is seriesresonant at the frequency of said waves, two opposite projections andopposed plates at the inner ends thereof which constrict the width ofsaid aperture, and means for adjusting the spacing between said plates.

References (Iited in the file of this patent UNITED STATES PATENTS2,106,771 Southworth Feb. 1, 1938 2,210,636 Schelkunotf Aug. 6, 19402,270,416 Cork Jan. 20, 1942 2,368,031 Llewellyn Jan. 23, 1945 2,408,435Mason Oct. 1, 1946

